Planar solar concentrator power module

ABSTRACT

A planar concentrator solar power module has a planar base, an aligned array of linear photovoltaic cell circuits on the base and an array of linear Fresnel lenses or linear mirrors for directing focused solar radiation on the aligned array of linear photovoltaic cell circuits. The cell circuits are mounted on a back panel which may be a metal back plate. The cell circuit area is less than a total area of the module. Each linear lens or linear mirror has a length greater than a length of the adjacent cell circuit. The cell circuit may have cells mounted in shingle fashion to form a shingled-cell circuit. In an alternative module, linear extrusions on the circuit element have faces for mounting the linear mirrors for deflecting sun rays impinging on each mirror onto the shingled-cells. The linear extrusions are side-wall and inner extrusions with triangular cross-sections. The circuit backplate is encapsulated by lamination for weather protection. The planar module is generally rectangular with alternating rows of linear cell circuits and linear lenses or linear mirrors.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/374,808 filed Apr. 24, 2002 and U.S. ProvisionalApplication No. 60/391,122 filed Jun. 25, 2002.

BACKGROUND OF THE INVENTION

[0002] Solar cells generate electricity but at a cost which is too highto compete with electricity from the electric power company. It isgenerally acknowledged that the solar panel cost will have to drop toapproximately $1 to $2 per installed Watt before solar cells can competein this large potential market. Today's cost for solar panels is in the$6 to $7 per Watt range. Three different approaches have been pursued inattempts to resolve this cost problem.

[0003] The conventional approach is to use large silicon solar cellstiled in planar modules where the cell area represents over 80% of thetotal panel area. The cells in this approach can be single crystal orlarge grain polycrystalline cells. This approach represents over 90% ofthe market but the cost of this approach has bottomed out and no furthercost reductions are expected.

[0004] The second approach is based on the assumption that the cost ofsilicon wafers is too high and one needs to make low cost thin filmcells. The argument is that paint is cheap and that maybe a way can befound to make paints generate electricity. This thin film approachincludes amorphous silicon and small grain-size polycrystallinematerials like CuInSe2 and CdTe. The problem with this approach has beenthat destroying the crystal material degrades solar cell performance. Todate, this approach has not yielded modules costing less than $8 perWatt.

[0005] The third approach is based on concentrating the sunlight ontosmall single crystal cells using larger inexpensive plastic lenses ormetal mirrors. This approach allows more efficient cells to be used andmakes good technical sense. However, the problems with this approach arenot technical but instead relate to business and politics. Solving thebusiness problems inherent in this approach is the focus of thisinvention.

[0006] Serious attempts to develop solar concentrator photovoltaicsystems can again be divided into three parts. First, attempts have beenmade to use point focus lenses and 30% efficient cells where the systemsoperate at high concentration ratios, e.g. approximately 500 suns. Theproblem here is not with the technology. The various components work,and systems have been demonstrated. The problem here is that theinvestment required to create positive cash flow is too large. Largecompanies will not take the risk and small companies do not have theresources and the government is not helping. The 30% cells are not beingmanufactured and investment is required here. Furthermore, trackers withthe required accuracy are not being manufactured. Again investment isrequired. Investment is also required for the thermal management andlens elements. Finally, these systems are not cost effective unless madein large sizes and in large volumes and there are no intermediatemarkets other than the utility scale market.

[0007] The second approach to solar concentrators involves the use ofarched linear Fresnel lenses and linear silicon solar cell circuits.These systems are designed to operate at approximately 20 suns. This isalso a technically proven approach but this approach also suffers fromthe investment problem. Here, investment is again required for speciallenses, trackers, and thermal management systems. Here, the plan is thatthe cells will be available from the cell suppliers who make planararrays. However, this presents two problems. The first problem is thatthe planar cells have to be significantly modified to operate at 20suns. The second problem is that the planar cell suppliers are notmotivated to cooperate. For example, suppose that the concentratorapproach proves to be cheaper and the market expands by three times. Theproblem for the planar cell suppliers is that their part will actuallyshrink by {fraction (3/20)} times. Again, these systems are not costeffective unless made in large sizes and in large volumes and there areno intermediate markets other than the utility scale market.

[0008] The third approach to solar concentrator systems was initiated bythe planar module manufactures. Realizing that if their one sun planarmodule were operated at 1.5 suns, they could produce 1.5 times morepower and consequently reduce the cost of solar electricity by 1.5times, they built a system using edge mirrors to deflect sunlight fromthe edge areas onto their panels. Unfortunately, this approach wastechnically naive. The problem encountered was that the modules thenabsorbed 1.5 times more energy and there was no provision to remove theadditional heat. This then affected the module lifetime.

[0009] Solar concentrators require very high investments to scale upproduction of a new concentrator cell. The investment required formanufacturing scale-up versions of a new cell is prohibitive. Anotherproblem that needs to be solved is the cell-interconnect problem.

[0010] There is a need for a solar concentrator module that is aretrofit for a planar module and that is easier and cheaper to make. Thebusiness infrastructure for trackers and lenses should already bein-place. The heat load should be easily manageable. Investmentrequirements should be manageable and it should not threaten existingcell suppliers. Cells to be used should be available with very minorchanges relative to planar cells. Therefore, low cost cells should beavailable from today's cell suppliers. Finally, it should be usable inearly existing markets in order to allow early positive cash flow.

SUMMARY OF THE INVENTION

[0011] The present invention addresses and resolves the above needs.FIGS. 1, 2, and 3 show a preferred planar concentrator solar powermodule. The unit depicted measures, but is not limited to, 25″ by 40″ by3.25″ deep. The size depicted is exemplary and is similar to 75 W planarmodules manufactured by Siemens, Kyocera, and Solarex. All of thesemodules measure approximately 25″ by 40″ and produce about the samepower. Other sizes are also within the scope of this invention.

[0012] The conventional planar modules consist of large silicon cellssandwiched between plastic sheets with a glass front plate surrounded bya 2″ thick metal frame, for example aluminum frame, for rigidity. Ourpreferred planar concentrator solar module consists of a back metalsheet upon which linear silicon cell circuits are mounted. In theembodiment depicted, there are plural circuits, as for example but notlimited to, 6 circuits containing cells approximately 1.3″ or 1.2″ wide.The circuit separation is, for example, 4″ or 3.6″. Therefore, the cellarea represents one third of the total module area resulting in a majorcost reduction for cells.

[0013] In the preferred module, as an example, a 3.25″ thick metalframe, for example, aluminum frame, surrounds the module with the cellsmounted on the back panel. A lens array is mounted on a glass sheetforming the front side of the planar concentrator solar module. Thereare, for example, 6 linear Fresnel lenses on this front sheet with eachlens being, for example, about 3.6″ or about 4″ wide and aligned suchthat the solar rays from each lens impinge on a linear power circuit. Inthe exemplary case, there are 6 lenses and 6 aligned circuits. Otherconfigurations with more or less lenses and more or less circuits arewithin the scope of this invention. Alternatively, several of thesegoals may be accomplished using linear extruded elements with mirroredfaces.

[0014] The modules are manufactured at a cost below today's module cost.A price in the $3 to $4 per Watt range, below the present $6 to $7 perWatt range, and subsequently, at the $1 to $2 per Watt range, istargeted. A successful 3-sun module results in a larger investmentenabling the $1 to $2 per Watt target to be eventually achieved with 30%efficient concentrator cells operating at higher concentration ratios.

[0015] Applicants have previously described a similar linear lens andlinear circuit configuration for a different set of applications. Inthat disclosure, we noted that the preferred pointing requirement forthis design is very broad, being greater than +/−5 degrees in bothdirections. One preferred embodiment of that device incorporates Fresnellenses and silicon solar cells. For example, a 6″×8″ solar batterycharger, about 2.5″ thick may yield about 4 W. It can collapse to about{fraction (1/2)}″ thickness for easy transportation. Angle tolerancealong the circuit length/direction is about +/−20 degrees whichcorresponds to over two hours between alignments. For example, if onesets the circuits vertical in the early morning and late afternoon, andhorizontal in the midday, the device will require 3 alignments in aneight-hour period. 30% efficient cells of about 8″×12″ yield 16 W.

[0016] Advantages of the present planar solar concentrator power moduleinclude, but are not limited to, the following:

[0017] 1. The cells are mounted in rows on a metal back plate with therows close enough to each other that the heat can spread in the backplate so that the air cooling area is similar to that of the standardplanar module.

[0018] 2. The cells used may be obtained from several different planarcell suppliers requiring only a minor change in grid design, for examplechanges in size and front metal pattern, to operate at 2-3 suns.

[0019] 3. The linear circuit assembly may be automated leading to afurther cost savings relative to traditional planar module assembly,which is presently, labor intensive.

[0020] 4. The thermal management is easily handled. The heat spreads inthe back metal plate such that the air contact area for heat removal isthe same as the lens area. This means that the heat removal isequivalent to the planar module case.

[0021] 5. There are already several Fresnel lens suppliers. Theconcentration ratio is low and not technically challenging. The lensesshould be low cost when made in high volume.

[0022] 6. The modules are designed such that the elongated dimension,the cell rows, and the linear concentrator elements are oriented alongthe North-South direction with the linear concentrator elements beinglonger than the cell rows so that the modules can be mounted on singleaxis trackers without requiring seasonal adjustments.

[0023] 7. The modules operate at low concentration on simple single-axistrackers requiring pointing tolerance of no less than +/−2 degrees.

[0024] 8. This unit resembles smaller units in design and assembly andcan be used in different devices such as, but not limited to, solarbattery chargers for cell phones, digital cameras, PDAs such as, but notlimited to, the Palm Pilot, laptop computers, etc.

[0025] 9. The planar modules and the concentrator modules are similar inform and function.

[0026] 10. The concentrator module unit operates at two-suns orthree-suns using one-half or one-third the silicon solar cell arearelative to traditional planar panels thus leading to a major costsavings.

[0027] 11. The cells used can be obtained from several different planarcell suppliers requiring only a minor change to operate at two-suns orthree-suns.

[0028] 12. The concentration ratio is low and not technicallychallenging. Extruded linear elements with mirrored faces are low cost.

[0029] 13. The tracking accuracy requirement is minimal. This means thatcommercially available liquid refrigerant trackers from Zomeworks can beused.

[0030] 14. The Zomeworks trackers are presently used with planar solarmodules for farm irrigation systems. This means that there is animmediate intermediate market with marketing channels alreadyestablished.

[0031] 15. The fact that this unit resembles a traditional planar solarmodule will lead to easy customer acceptance. Thereafter, it would leadto an even more lower cost, higher concentration ratio systems.

[0032] These and further and other objects and features of the inventionare apparent in the disclosure, which includes the above and ongoingwritten specification, with the claims and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 shows a top view of the planar solar concentrator powermodule of the present invention.

[0034]FIG. 2 shows a cross section through the planar solar concentratorpower module of FIG. 1.

[0035]FIG. 3 shows a blow up section from FIG. 2 with a single lens andcircuit element in more detail.

[0036]FIG. 4 is a side view of a smaller planar solar concentrator powermodule with two lens and circuit elements.

[0037]FIG. 5 shows a top view in which the lenses magnify the circuitsof the power module of FIG. 4.

[0038]FIG. 6 shows a section of the back metal sheet with embossedterraces in fabricated linear circuits.

[0039]FIG. 7 shows a shingle circuit in which the cells are mounted inthe terraces of FIG. 6 in a shingle fashion.

[0040]FIG. 8 shows a perspective view of a planar solar concentratorpower module. Note however, as shown in FIG. 5, the lens effect ismerely exemplary.

[0041]FIG. 9 shows several planar solar concentrator power-modulesmounted on a solar tracker.

[0042]FIG. 10 shows a 3D view of the planar solar concentrator powermodule of the present invention with mirror elements.

[0043]FIG. 11 shows a cross-section through the planar solarconcentrator power module of FIG. 10 at A-A.

[0044]FIG. 12 shows a blow up section from FIG. 11 showing a circuitelement and two types of linear extrusions with mirrored faces.

[0045]FIG. 13A shows a commercial planar cell.

[0046]FIG. 13B shows the cell of FIG. 13A cut up into four 2×concentrator-cells.

[0047]FIG. 13C shows the cells reassembled into a shingled-cell circuitelement.

[0048]FIG. 14 shows two shingled-cell circuit elements mounted on theheat spreader metal back-plate with a stress relief ribbon bond betweenthe circuit elements.

[0049]FIG. 15 is a top view of two series connected standard planarcells.

[0050]FIG. 16 is a top view of two series connected standard planarcells cut in half and mounted in a 2-sun concentrator mirror module.

[0051]FIG. 17 is an end view of the cell and module of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052]FIGS. 1, 2, 3, and 8 show a preferred planar concentrator solarpower module 1. FIG. 1 shows a top view of the planar solar concentratorpower module 1 of the present invention. An array 3 of linear Fresnellenses 5 produces lines of focused solar radiation that fall on analigned array of linear photovoltaic power circuits. FIG. 2 shows across section through the planar solar concentrator power module 1 ofFIG. 1. The cross section is perpendicular to the focal lines producedby the lenses and perpendicular to the circuit length dimension. FIG. 3shows a blow up section from FIG. 2 showing a single lens 21 and circuitelement 23 in more detail.

[0053] The preferred unit depicted is exemplary with dimensions notlimited to the following. For example, the preferred unit may measure25″ by 40″ by 3.25″ deep. The size depicted is exemplary and is similarto 75 W planar modules manufactured by Siemens, Kyocera, and Solarex.All of these modules measure approximately 25″ by 40″ and produce aboutthe same power. The planar modules consist of large silicon cellssandwiched between plastic sheets with a glass front plate surrounded bya 2″ thick metal frame, for example aluminum frame for rigidity. Otherdimensions are well within the scope of this invention.

[0054] The preferred planar concentrator solar module consists of a backpanel of metal sheet 25 upon which linear silicon cell circuits 7 aremounted. In the exemplary embodiment depicted, there are, for examplebut not limited to, 6 lenses and 6 aligned circuits containing, forexample, cells 23 about 1.3″ or about 1.2″ wide. The circuit separationis, for example, about 4″ or 3.6″. Therefore, the cell area representsone third of the total module area resulting in a major cost reductionfor cells.

[0055] In the preferred module, for example, about a 3.25″ thick metalframe 9, for example aluminum frame, surrounds the module 1 with thecells 23 of the cell circuits 7 mounted on the back panel 25. A lensarray 3 is mounted on a glass front sheet 27 forming the front side ofthe planar concentrator solar module 1. There are, for example, 6 linearFresnel lenses 5 on this front sheet 27 with each lens 21 being, forexample, 4″ wide and aligned such that the solar rays from each lens 21impinge on a linear cell circuit 7 connected to a power circuit assembly11 with +/−terminals 13. In the FIG. 1 example, there are 6 lenses and 6aligned circuits. Other lens and circuit combinations are within thescope of this invention.

[0056] A preferred lens 5 has, for example, a lens width and circuitspacing of approximately 4″ or 3.6″. Given a lens width of 4″ or 3.6″,the shortest reasonably achievable focal length will be approximately 4″or 3.6″ respectively. If, then, the lens is set to a cell spacing, forexample, at 3.25″ or 3″, the focal line on the circuit will beapproximately 0.75″ or 0.7″ wide. For a cell width of 1.3″ or 1.2″,there will be an illuminated region of 0.75″ or 0.7″ wide and dark bandson either side of (1.3−0.75)/2=0.28″ or (1.2−0.7)/2=0.25″ width. Thesedark regions will allow a tracking band of tan⁻¹(0.28/3.25)=+/−5 ortan⁻¹(0.25/3)=+/−5 degrees wide. We choose this tracking band toleranceprecisely because this is the tracking tolerance of the commerciallyavailable Zomeworks tracker. The same applies for the 2× mirror module.

[0057] A lens width of 4″ provides several advantages, Firstly, the 4″width allows for a panel thickness of 3.25″, not too much thicker than astandard planar solar panel (2″). Secondly, the 4″ width is advantageousfor thermal management. The lenses 5 concentrate the solar energy intothe circuits 7. The waste heat then is transferred to the metal backplate 25. It then spreads laterally through the metal such that themetal plate temperature is nearly uniform. If the spacing betweencircuits is too large, the heat will not spread uniformly and thecircuits will run too hot. A 4″ or 3.6″ spacing does allow for a uniformplate temperature with a reasonably thin and light back metal plate. Thesame also applies for the 2× mirror module.

[0058] The linear Fresnel lenses 5 provide several advantages. The firstrelates to seasonal alignment. The sun's midday position moves north andsouth+/−23 degrees from summer to winter. This movement is accommodatedusing a linear lens 21 by making the lens length longer than the circuit23 length and aligning the lens focal line in the north/south direction(see, for example, FIG. 1). In the present module 1, the circuits 7 are,for example but not limited to, about 1.4″ or 1.3″ shorter than the lens5 at both ends 15, 17. This gives a tracking tolerance in thenorth/south direction of tan⁻¹(1.4/3.25)=+/−23 degrees or tan⁻¹(1.3/3)=+/−23 degrees, respectively.

[0059] The second reason for the having the linear Fresnel lenses 5 isthat they lead to linear power circuits 7 and a linear power circuitassembly 37 (FIG. 7) can be automated.

[0060]FIGS. 4 and 5 are examples of a smaller planar solar concentratorpower module 31 with two lens and circuit elements 33. The FIG. 4 powermodule 31 shows the unit from a side view whereas FIG. 5 shows thelenses magnifying the circuits from the top view. The FIG. 5 powermodule 31 is presented to show the lens magnification effect.

[0061]FIGS. 6 and 7 show one example of fabricating the linear circuits.FIG. 6 shows a section of the metal back sheet 25 with embossed terraces35. FIG. 7 shows the cells mounted in these terraces in a shinglefashion 37 with the back edge 39 of one cell 41 overlapping the frontedge 43 of the previously placed cell 45.

[0062] The cell design is typical for solar cells having complete metaldeposited on the backside with a grid pattern on the front. In thiscase, the grid lines run in the circuit direction and connect to a busbar on one edge of the top of the cell. The bus electrically connects tothe back metal of the next cell. In this way, a front to back seriesconnection is made between cells to make shingle circuits.

[0063] As shown in FIG. 1, there are circuit terminal pads 49 at the endof each circuit. Insulated metal elements, such as but not limited to,ribbons 47 and 51 connect these circuits to plus and minus panelterminals 13.

[0064] As shown in FIG. 3, an insulating film 53 (as for example paint)may be placed over the metal back plate 25 so that the circuit 7 is ingood thermal contact with the metal back plate but not in electricalcontact with the back plate.

[0065] We have previously described shingle circuits in the context ofthermophotovoltaics. An important consideration for shingle circuits isthat the coefficient of thermal expansion (CTE) of the metal back plateshould be matched with the coefficient of thermal expansion of the cellsso that the electrical connecting bonds between cells are not pulledapart as the module heats or cools. With matched CTES, the cells andmetal back plate expand and contract together with changes intemperature. In the case of silicon solar cells, an appropriate metalmay be, for example but not limited to, alloy 42 (Fe 58%, Ni 42%).

[0066] The shingle circuit assembly 37 depicted here is not the only wayin which linear circuits 7 can be fabricated. Other fabrication methodsare within the scope of this invention. For example, ribbon leads can berun from the back of one cell to the front of the next cell. Loops inthe ribbon connections will allow for differences in CTEs so that analuminum back plate may then be used. This assembly procedure can beautomated although with more steps than for the shingle circuitfabrication sequence. Either circuit type, and assembly process, fallswithin the scope of the present invention.

[0067]FIG. 8 shows a perspective view of a planar solar concentratorpower module 1. Note however, as shown in FIG. 5, the lens effect is notrealistically depicted.

[0068]FIG. 9 shows several planar solar concentrator power-modules 1mounted on a solar tracker 55. The present planar solar concentratorpower module may be provided in solar powered water pumping deviceswhich is used for irrigation worldwide. The advantages of the presentmodule design include, but are not limited to, cheaper costs ofproduction because it uses less expensive single crystal material, andeasy availability and adaptability for immediate replacements in severaldifferent applications.

[0069] A preferred planar concentrator photovoltaic module comprises aplanar array of linear Fresnel lenses in front of and aligned with aplanar array of linear circuits. The circuits are mounted on a metalsheet allowing for heat spreading and heat removal.

[0070] The planar concentrator photovoltaic module further compriseslenses which are longer than the circuits such that the acceptance anglefor sunlight in the length dimension is greater than or equal to 20degrees allowing for polar axis tracking without seasonal adjustments.

[0071] The planar concentrator photovoltaic module comprises lens havingwidths about three times larger than the width of the cell and circuit.The image from the lens underfills the cells with dark bands on thecells on either side of the image allowing for the acceptance angle forsunlight in the width dimension to be greater than or equal to about 5degrees.

[0072] The planar concentrator photovoltaic module further comprises ametal sheet upon which the circuits are mounted the metal sheet has acoefficient of thermal expansion compatible with the coefficient ofthermal expansion of the cells. The metal sheet is embossed withterraces upon which the cells are mounted in a linear shingle circuit.

[0073]FIGS. 10, 11, and 12 show the planar concentrator solar powermodule of the present invention. FIG. 10 shows alternating rows oflinear shingled-cells and linear mirror elements where the mirrorsdeflect sun rays down to the cells. FIG. 11 shows a cross-sectionthrough the planar solar concentrator power module of FIG. 10 at A-A.The cross-section is perpendicular to the rows of cells and mirrors.FIG. 12 shows a blow-up section from FIG. 11 showing a circuit elementand, as examples, two types of linear extrusions: the module side wallextrusion and the inner extrusions with triangular cross-sections.

[0074] A preferred unit measures, for example, about 20″ by 44″ by 3.25″deep, preferably 21″ by 47″ by 3.25″ deep. The size depicted isexemplary and is similar to 75 W one-sun planar modules manufactured byBP Solar, Siemens, Kyocera, and Solarex. All of these one-sun modulesmeasure approximately 20″ by 44″ or about 21″ by 47″ and produce aboutthe same power. The one-sun planar modules consist of large siliconcells sandwiched between plastic sheets with a glass front platesurrounded by a 2″ thick aluminum frame for rigidity.

[0075] The present planar concentrator solar module 100 consists of aback panel 103, preferably of metal sheet, upon which linearsilicon-cell circuits 105 are mounted. In the example shown, there arefour circuits containing cells 107 approximately 2.5″ wide. Thepreferred circuit separation is approximately 5″. Therefore, the cellarea represents one half of the total module area resulting in a majorcost reduction for cells. In the exemplary module, an approximately3.25″ thick aluminum frame 122 with end plates 123 surrounds the modulewith the cells mounted on the back panel 103.

[0076] Mirrors 109 are located between the rows of linear silicon-cellcircuits 105. Referring to FIGS. 11 and 12, the mirrors 109 are mountedon the faces 111, 113 of the exemplary two types of linear extrusions115, 117. Sun rays hitting each mirror 109 are deflected down onto thecells 107. The two types of linear extrusions are the module side-wallextrusions 115, and the inner extrusions with triangular cross-section117.

[0077] The present module shown is mechanically assembled as follows.Cells 107 are first mounted on the metal heat spreader plate 103. Forlow cost, the cells 107 are mounted in shingled-cell circuits 105. Theheat spreader plate 103 is captured in slots 119 in the side wallextrusions 115. There are fastener holes 121 running from end to end inboth types of extrusions 115, 17. Fasteners such as, but not limited to,sheet metal screws 120 (FIG. 10) running through holes 121 in end plates123 (FIG. 10) connect all of the elements together.

[0078] As noted above a problem for solar concentrators has been thehigh investment required to scale up production of a new concentratorcell. Therefore, it is desirable to use planar solar cells that arealready in high volume production at low cost. FIGS. 13A-C show how toproduce the solar concentrator cells 130 at low costs by simply cuttinga commercial planar cell 132 into four parts. FIG. 13A shows acommercial planar cell 132. FIG. 13B shows the cell of FIG. 13A cut upinto four 2× concentrator-cells 130. FIG. 13C shows the cellsreassembled into a shingled-cell circuit element 134.

[0079] Another problem solved by the invention is the cell-interconnectsfor concentrator modules. A standard one-sun planar module typically hasthirty-six 5″ square cells. While the present concentrator module hashalf the cell area, each cell is one quarter the area of a planarone-sun cell. Therefore, there are twice the number of cells or 72cells. If stitch ribbon bonds from cell to cell are used, as is typicalfor planar modules, twice the number of bonds will be required, whichwill increase assembly cost. This problem is resolved by makingshingled-cell circuit elements 134 as shown in FIGS. 13B, 13C, and 14.

[0080]FIG. 13C shows a top view of an exemplary shingled-cell element134 containing four cells. FIG. 14 shows the side view of a circuit row136 containing two shingled-cell circuit elements 134 mounted on theheat spreader metal back-plate 138 with stress relief ribbon bonds 40between circuit elements 134. In a shingled-cell element 134, cells 142are mounted in a shingle fashion with the back edge 144 of one celloverlapping the front edge 146 of the previously placed cell. Theshingled-cell design is used for solar cells having a complete metaldeposited on the backside with a grid and bus pattern on the front. Inthis case, the bus runs in the circuit direction. The bus electricallyconnects to the back metal of the next cell. In this way, a front toback series connection is made between cells to make shingle circuitelement. There are half as many bonds used for shingled-cell circuits aswhen stitch ribbons are used from cell to cell.

[0081] As pointed out above, an important consideration for shinglecircuits is that the coefficient of thermal expansion (CTE) of the metalback plate should be matched with the coefficient of thermal expansionof the cells so that the electrical connecting bonds between cells arenot pulled apart as the module heats or cools. With matched CTEs, thecells and metal back plate expand and contract together with changes intemperature. In the case of silicon solar cells, an appropriate metalmay be alloy-42 (Fe 58%, Ni 42%).

[0082] It is also possible to use shingled-cell elements even if thereis not a perfect CTE match between the cells and the metal backingplate. This is done by providing flexibility in the adhesive 148 used tobond the cells 142 to the metal back plate and by providing periodicstress relief ribbon bonds 140. FIG. 14 shows a stress relief ribbonbond 140 between two shingled-cell circuit elements 134. Cells in theback panel may be protected by lamination with a transparent encapsulant149. Lamination may be, but is not limited to, a transparent plasticsheet covered by a transparent Teflon sheet or a glass plate as used inthe planar modules.

[0083] Another problem is to determine how often stress relief ribbonbonds 140 are required. The present invention provides a solution tothis problem. For example, 4″ long Si cells have been mounted withflexible thermally conductive adhesive to aluminum plates and operatedfor ten years in a solar concentrator prototype without failure. The CTEdifference between aluminum and silicon is (22−4)×10⁻⁶ per C. In thepresent invention using a carbon steel back plate with a CTE differenceof (11−4)×10−6 per C, or 2.5 times less, uniquely allows for the use ofa shingled-cell element 2.5 times longer than 4″ or 10″ long, as shownin FIG. 14.

[0084] The invention addresses the high-cost problems for solarconcentrators requiring scale up production of new concentrator cells.FIGS. 15, 16, and 17 show how to use planar solar cells already in highvolume production in the present modules. The present solar concentratorcells are formed by cutting up commercial planar cells into halves.

[0085] In the 2× mirror module, as shown in FIGS. 15, 16, and 17, planarcells 150 are cut in half 152, separated by mirror elements 166 andoperated at 2× concentration with the mirrors. Thus half the number ofplanar cells 154, 156 are used to form a module 160 with the same power.Also, a further advantage is that half the number of ribbon bonds 158are required. Ribbon bonding techniques are similar to the planar modulerequiring no additional equipment nor manpower for mirror modulefabrication.

[0086] The metal back plate 162 with linear circuits 164 are formed asshown in FIGS. 16 and 17. After the cells 150 are cut and ribbon bonded158 front to back, the circuit strings 168 are bonded to the metal backplate 162 with thermally conductive epoxy 170. The circuits 164 areelectrically isolated from the metal back plate. After the circuits 164are bonded to the metal back plate 162 and wired together, the cells inthe back panel are then protected by lamination with a transparentencapsulant. Lamination may be, but is not limited to, a transparentplastic sheet covered by a transparent Teflon sheet or a glass plate asused in the planar modules, as shown at 149 in FIG. 14.

[0087] The interconnect procedures for connecting ribbons to cells frontto back is similar to that used in the planar modules. The ribbonconnections are labor intensive and therefore alternative ways may beused for the interconnections. For example, shingled cell circuits aremade as shown in FIGS. 13A-C and 14, which enables a faster cell-circuitassembly using automated equipment.

[0088] The present cell and mirror height dimensions are preferablybetween 2″ and 3″, more preferably 2.5″. That allows for a panelthickness of about 3.25″, not too much thicker than a standard planarsolar panel with thickness of about 2″. Also, it provides optimalthermal management. The mirrors concentrate the solar energy into thecircuits. The waste heat then is transferred to the metal back plate. Itthen spreads laterally through the metal such that the metal platetemperature is nearly uniform. If the spacing between circuits is toolarge, the heat will not spread uniformly and the circuits will run toohot. A preferred spacing of about 5″, or about 2.5″ from cell edge tothe next cell edge, allows for a uniform plate temperature with areasonably thin and light back metal plate.

[0089] Linear circuits and mirrors provide several advantages. Firstly,aluminum extrusions and linear shingled circuits are easy to make.Secondly, it provides for optimal seasonal alignment. The sun middayposition moves north and south+/−23° from summer to winter. Thismovement is accommodated using a linear mirror by making the mirrorlength longer than the circuit length and aligning the mirror focal linein the north/south direction. The present module circuits are about 1.4″shorter than the mirrors at both ends which uniquely gives a trackingtolerance in north/south direction of tan⁻¹(1.4/3.25)=+/−23°.Preferably, providing circuits shorter by about 1.2″ than the mirrors atboth ends gives tracking tolerance in the north/south direction oftan⁻¹(1.2/2.5)=+/−25°.

[0090] The invention also provides pointing tolerance in the east/westdirection. If the mirror tilt angle referenced to the normal from thecell plane is 30°, then all of the rays reflected by the mirrors willfall on the cells as long as the module is precisely pointed at the sun.This invention provides a pointing tolerance of approximately +/−2°translating to a mirror tilt off-normal angle of approximately 26°.

[0091] The present invention allows for the manufacture of modules at acost below today's module cost. Target prices are in about the $3 to $4per Watt range, preferably at about the $1 to $2 per Watt cost range,well below the $6 to $7 per Watt price range of present modules.

[0092] While the invention has been described with reference to specificembodiments, modifications and variations of the invention may beconstructed without departing from the scope of the invention, which isdefined in the following claims.

We claim:
 1. A planar concentrator solar power module apparatuscomprising a planar base, an aligned array of linear photovoltaic cellcircuits on the base and an array of linear planar Fresnel lenses abovethe base for directing focused solar radiation on the aligned array oflinear photovoltaic cell circuits.
 2. The apparatus of claim 1, whereinthe cell circuits further comprise plastic sheets and silicon cellssandwiched between the plastic sheets.
 3. The apparatus of claim 2,further comprising a glass front plate and a frame surrounding the glassfront plate.
 4. The apparatus of claim 3, wherein the frame is analuminum frame.
 5. The apparatus of claim 3, wherein the base furthercomprises a back panel and wherein the cell circuits are mounted on theback panel.
 6. The apparatus of claim 5, wherein the back panel is ametal plate.
 7. The apparatus of claim 1, wherein an area of the cellcircuits is less than a total area of the module.
 8. The apparatus ofclaim 7, wherein the area of the cell circuits is one half the totalarea of the module.
 9. The apparatus of claim 7, wherein the area of thecell circuits is one third the total area of the module.
 10. Theapparatus of claim 3, wherein the array of linear Fresnel lenses ismounted on a bottom of the glass front plate forming a front side of themodule.
 11. The apparatus of claim 10, wherein the array of Fresnellenses comprises plural lens, each lens having an adequate size andspaced alignment from the cell circuits for sufficiently concentratingenergy from sun rays into an adjacent cell circuit.
 12. The apparatus ofclaim 11, further comprising a power circuit assembly connected to thecell circuits.
 13. The apparatus of claim 11, wherein each linear lenshas a length greater than a length of the adjacent cell circuit.
 14. Theapparatus of claim 13, wherein a focal line of each lens is aligned in anorth/south direction.
 15. The apparatus of claim 12, wherein the powercircuit assembly is a linear power circuit assembly.
 16. The apparatusof claim 2, wherein the aligned array of the cell circuits is ashingle-circuit array.
 17. The apparatus of claim 16, wherein theshingle-circuit array comprises a metal back sheet with embossedterraces, and wherein the cells are mounted in the terraces in ashingle-fashion wherein a back edge of one cell overlaps a front edge ofa previous cell.
 18. The apparatus of claim 17, wherein theshingle-circuit array further comprises metal deposits on a backside, agrid pattern on a front side and a bus bar connected to an edge of a topof the cell circuits.
 19. The apparatus of claim 18, wherein the bus baris electrically connected to a back metal of an adjacent cell forming afront to back series connection between the cells and thereby formingshingle circuits.
 20. The apparatus of claim 19, further comprisingcircuit terminal pads at an end of each circuit.
 21. The apparatus ofclaim 20, further comprising insulated metal elements connecting thecircuits to plus and minus panel terminals of a power circuit.
 22. Theapparatus of claim 21, further comprising an insulating film on themetal back sheet enabling good thermal non-electrical contact betweenthe circuit and the metal back plate.
 23. The apparatus of claim 22,wherein a coefficient of thermal expansion of the metal back sheet ismatched with a coefficient of thermal expansion of the cells for matchesand uniform expansion of the cells and the metal back sheet in responseto changes in temperature.
 24. The apparatus of claim 23, wherein thecells are silicon cells and the metal back sheet is of an alloymaterial.
 25. The apparatus of claim 24, wherein the alloy material isalloy 42 comprising Fe 58% and Ni 42%.
 26. The apparatus of claim 19,wherein the front to back series connection comprises ribbon leadsrunning from a back side of one cell to a front side of an adjacent nextcell and loops in the ribbon leads for allowing differences incoefficient of thermal expansion between the cells and the metal backsheet.
 27. A planar concentrator photovoltaic module comprising a planararray of linear circuits, a planar array of linear Fresnel lensesdisposed in front of and aligned with the planar array of linearcircuits, and a metal sheet forming a base for mounting the planar arrayof linear circuits for allowing heat spreading and heat removal.
 28. Themodule of claim 27, wherein the lenses are longer than the circuits suchthat an acceptance angle for sunlight in a length dimension is greaterthan or equal to 20 degrees for allowing polar axis tracking withoutseasonal adjustments.
 29. The module of claim 28, wherein lenses havewidths about three times larger than a width of the cell circuits,wherein an image from the lens underfills cells in the cell circuitswith dark bands on either side of the image allowing for the acceptanceangle for sunlight in a width dimension to be greater than or equal toabout 5 degrees.
 30. The module of claim 29, wherein the metal sheet hasa coefficient of thermal expansion compatible with a coefficient ofthermal expansion of cells in the cell circuits.
 31. The module of claim30, wherein the metal sheet has embossed terraces for mounting the cellsin a linear shingle circuit.
 32. A planar concentrator solar powermodule apparatus comprising a circuit element, rows of series connectedsolar cells in the circuit element, and linear mirrors in the circuitelement for deflecting sun rays to the rows of solar cells.
 33. Theapparatus of claim 32, wherein the circuit element comprises linearextrusions.
 34. The apparatus of claim 33, wherein the linear extrusionsinclude side wall extrusions are disposed along boundaries of thecircuit element.
 35. The apparatus of claim 34, wherein the linearextrusions include inner extrusions having triangular cross-sections.36. The apparatus of claim 35, further comprising a back panel in thecircuit element.
 37. The apparatus of claim 36, wherein the back panelis a metal sheet.
 38. The apparatus of claim 37, wherein the rows ofsolar cells are linear silicon-cell circuits mounted on the metal sheet.39. The apparatus of claim 38, further comprising a metal frame and endplates surrounding the circuits.
 40. The apparatus of claim 32, whereinan area of the cells is less than a total area of the module.
 41. Theapparatus of claim 39, wherein the mirrors are disposed between rows ofthe linear silicon-cell circuits.
 42. The apparatus of claim 41, furthercomprising linear extrusions on the circuit element, and wherein themirrors are mounted on faces of the linear extrusions for deflecting sunrays impinging on each mirror onto the linear silicon-cell circuits. 43.The apparatus of claim 42, wherein the linear extrusions includeside-wall extrusions.
 44. The apparatus of claim 42, wherein the linearextrusions include inner extrusions with triangular cross-sections. 45.The apparatus of claim 43, further comprising slots in the side wallextrusions, wherein the back panel is coupled to the slots in the sidewall extrusions.
 46. The apparatus of claim 42, further comprising endto end fastener openings in the linear extrusions and fasteners disposedin the fastener openings for coupling the circuit element, the linearmirrors on the linear extrusions, the back panel and the end plates. 47.The apparatus of claim 46, wherein the linear silicon-cell circuits aremounted on the metal back plate with stress relief ribbon bonds betweenthe cells.
 48. The apparatus of claim 42, further comprising cells withmetal deposits on a back side, a grid and bus on a front side, whereinthe bus electrically connects to a back metal of an adjacent cellforming a front to back series connection between cells thereby formingshingle-circuit elements.
 49. The apparatus of claim 47, wherein theback plate is a carbon steel back plate.
 50. The apparatus of claim 48,further comprising laminating capsule for encapsulating theshingled-cell circuit element.
 51. The apparatus of claim 50, whereinthe laminating capsule comprises a transparent material.
 52. Theapparatus of claim 51, wherein the transparent material is a plasticsheet.
 53. The apparatus of claim 52, further comprising a transparentcover.
 54. The apparatus of claim 53, wherein the transparent cover is aglass plate.
 55. The apparatus of claim 53, wherein the transparentcover is a teflon sheet.
 56. A method of assembling a planarconcentrator solar power module comprising mounting photovoltaic cellson a metal heat spreader back plate and forming a circuit element,connecting the cells in series to form linear circuit rows, mountinglinear mirrors on the plate, alternating the linear circuit rows and thelinear mirrors in the circuit element, deflecting sun rays with thelinear mirrors on to the linear circuit rows, concentrating solar energyinto the linear circuit rows and providing optimal thermal energymanagement.
 57. The method of claim 56, further comprising transferringwaste heat generated from the concentrating solar energy to the metalback plate, spreading the waste heat laterally through the metal plateand causing a temperature of the metal plate to be uniform.
 58. Themethod of claim 56, wherein the mounting the cells on the metal platecomprises providing adequate spacing between alternating circuits andallowing a temperature of the metal back plate to be uniform.
 59. Themethod of claim 56, further comprising mounting linear extrusions on themetal back plate and mounting the linear mirrors on faces of the linearextrusions and mounting the linear circuit rows between the mirrors. 60.The method of claim 59, further comprising allowing for optimal seasonalalignment by providing linear mirrors longer than the linear circuitrows, aligning the mirror focal line in a north/south direction andgiving a tracking tolerance in north/south direction corresponding to amovement of the sun.
 61. The method of claim 60, further comprisingallowing for a pointing tolerance in a east/west direction by providinga mirror tilt off-normal angle corresponding to a tracking movement ofthe sun.
 62. The method of claim 61, wherein the off-normal angle isabout 26°.
 63. A planar concentrator solar power module apparatuscomprising a planar metal base, an aligned array of linear photovoltaiccell circuits on the metal base, an aligned array of linear concentratorelements for directing solar radiation on the aligned array of linearphotovoltaic cell circuits, the linear photovoltaic circuits being inthermal contact with the metal base and being electrically isolated fromthe metal base, wherein an area of the metal base is equal to a totalmodule area for efficient heat spreading and heat removal.
 64. A planarconcentrator solar power module apparatus comprising a planar metalbase, an aligned array of linear photovoltaic cell circuits on the metalbase, an aligned array of linear concentrator elements for directingsolar radiation on the aligned array of linear photovoltaic cellcircuits, wherein the linear concentrator elements are longer than thelinear photovoltaic cell circuits.
 65. The apparatus of claim 64,wherein the linear photovoltaic cell circuits and the linearconcentrator elements are aligned along a North-South polar axis suchthat all cells in the linear photovoltaic cell circuits are uniformlyilluminated year around.